1. Field of the Invention
The present invention relates to a method of manufacturing an ink-jet printer head, which has an excellent workability to efficiently and quickly form (bore) good orifices in an orifice plate.
2. Description of the Related Art
Recently, ink-jet printers are widely used. The ink-jet printers include a thermal jet type which ejects ink droplets under the pressure of bubbles that are generated by heating the ink by means of a heat-generating resistor element and a piezoelectric type which ejects ink droplets by pressure that is applied to the ink by the deformation of a piezoelectric resistor element (piezoelectric element).
Because those types of printers do not require a developing step and transfer step and directly eject ink droplets on a recording medium to record information, they are advantageous over an electrophotographic type which uses powder-like toners in easy miniaturization and lower printing energy. The ink-jet printers are therefore popular particularly as personal printers.
The thermal jet type printer heads are classified into two structures depending on the ejection direction of ink droplets: a side-shooter type thermal ink-jet printer head which ejects ink droplets in a direction parallel to the heat generating surface of the heat-generating resistor element and a roof-shooter type or top-shooter type thermal ink-jet printer head which ejects ink droplets in a direction perpendicular to the heat generating surface of the heat-generating resistor element. The roof-shooter type thermal ink-jet printer head, in particular, is known for its very low power consumption.
FIGS. 1A through 1C exemplarily and schematically illustrate the printing principle of the roof-shooter type thermal ink-jet printer head. As shown in FIG. 1A, a heat-generating resistor element 2 is disposed on a silicon substrate 1, and an orifice plate 3 is adhered to an unillustrated partition and is so arranged as to face the silicon substrate 1. A plurality of orifices 4 as ink-ejection nozzles are formed in the orifice plate 3 at a location facing the heat-generating resistor element 2. Unillustrated electrodes are connected to both ends of the heat-generating resistor element 2, and ink 5 is always supplied to an ink flow path in which the heat-generating resistor element 2 is provided.
To eject ink droplets from the orifices 4, first, as shown in FIG. 1B, (1) energizing according to image information heats the heat-generating resistor element 2, thereby causing bubble nucleation on the heat-generating resistor element 2. (2) The generated bubbles are combined to generate a film bubble 6. (3) The film bubble 6 is adiabatically expanded and grown, pressing the nearby ink. This drives ink 5xe2x80x2 out of the orifices 4 so that the ink 5xe2x80x2 becomes an ink droplet 7 as shown in FIG. 1C which are ejected toward the surface of an unillustrated sheet of paper. (4) As the heat of the grown film bubble 6 is taken by the nearby ink, the film bubble 6 contracts. (5) The film bubble 6 disappears to be ready for the next heating of the heat-generating resistor element 2. This sequence of steps (1) to (5) is performed instantaneously.
One way of manufacturing such a thermal ink-jet printer head is to simultaneously form a plurality of heat-generating resistor elements, drivers for those elements and a plurality of orifices in a monolithic form by utilizing silicon LSI technology and thin film technology.
FIG. 2 presents a table illustrating steps of manufacturing such a thermal ink-jet printer head. As shown in FIG. 2, an oxide film, a resistor film and an electrode film are formed on a substrate in step (1). In step (2), the pattern of heat generating sections and the pattern of electrodes are respectively formed on the resistor film and the electrode film by photolithography or the like. In step (3), a partition is formed which separates the area on the substrate into a predetermined pattern, defining ink flow passages. In step (4), an ink feed passage and an ink feed hole are formed in the substrate. In step (5), an orifice plate is adhered onto the partition.
In step (6), a metal film is formed on the surface of the orifice plate and the pattern of orifices is formed on that metal film. In step (7), orifices are formed using an ordinary dry etching system, excimer laser or the like. In step (8), individual substrates collectively formed on a wafer are separated into individual units by dicing. In step (9), each single head substrate is bonded to a mount substrate with its leads connected to the associated leads thereof. This completes a practical unit of a thermal ink-jet printer head.
In the fabrication of a roof-shooter type thermal ink-jet printer head, the orifice plate should be adhered in such a way as not to bury the ink groove or ink passage formed by the partition with a height of about 10 xcexcm. While designing this partition to have a height of over 15 xcexcm eliminates the need for such a concern, the partition cannot be formed to a height of over 15 xcexcm by single application of a photosensitive resin which is the material for the partition. Applying the photosensitive resin twice however doubles the time for the step of forming the partition, thus lowering the working efficiency.
In addition, a high partition with a height of over 10 xcexcm makes it difficult to form fine ink flow passages that are needed for a head having a resolution of 400 dpi or greater. In this respect too, the height of the partition should be set to about 10 xcexcm at a maximum. Normally, an orifice plate which is prepared by applying an adhesive of an epoxy base or the like to a resin of polyimide or the like is adhered onto the partition by thermocompression bonding. This scheme requires that an adhesive should be applied to the thickness of, for example, 5 xcexcm or less just before usage and should be adhered to the substrate immediately thereafter. It is difficult to apply the adhesive uniformly and thin. Even if application of the adhesive to the thickness of 5 xcexcm is possible, the ink groove or ink flow passages after adhesion are narrowed to the height of 5 xcexcm by the adhesive that has been pressed from above by thermocompression bonding, so that part of the ink groove and ink flow passages may be blocked depending on a variation in the thickness of the adhesive.
The conventional scheme has a difficulty in applying an adhesive uniformly and thin and a technical problem on storage after application of the adhesive. It is therefore necessary to perform a work of adhering the orifice plate immediately after application of the adhesive. Further, because the adhesive is sticky, care should be taken to handle the partition applied with the adhesive at the time of adhering the orifice plate, i.e., the workability is not high. Even if polyimide which has a reliably high heat resistance is used for the partition and orifice plate as mentioned above, if an adhesive with a low heat resistance is used, deterioration of the adhesive during use would reduce the high heat-resistance reliability of the partition and orifice plate.
Recently, therefore, the aforementioned orifice plate 3 is acquired by forming an adhesive layer, which consists of a thermoplastic adhesive material having such a high glass transition point as not to flow at room temperature and excellent heat resistance, on the adhesion surface of a very thin polyimide film of about 30 to 40 xcexcm thick which is the essential material. This ensures storage of the orifice plate 3 with the adhesive material applied and allows the orifice plate to be easily adhered to the substrate 1 by thermocompression.
It is to be noted however that this thermoplastic adhesive layer should be adhered to both sides of the orifice plate 3, i.e., not only on the bottom of the orifice plate where the substrate 1 is to be placed but also on the top surface which does not inherently need such adhesion. This is because application of such an adhesive layer only on one side would cause warping or curling due to a difference in the coefficient of thermal expansion between the orifice body and the adhesive layer, making it troublesome to handle the orifice plate 3 and resulting in very poor working efficiency.
The orifice plate with a thickness of 30 to 40 xcexcm, though it is a very thin film member when it is handled, is still thick enough a member to form holes therein by using an ordinary dry etching system or excimer laser. It has therefore been difficult to simultaneously and adequately form multiple orifices in this orifice plate. Conventionally, orifices are formed in the orifice plate, the adequate number at a time, so that forming the whole orifices takes time.
To form multiple orifices at a time, dry etching with helicon wave plasma source (hereinafter referred to as xe2x80x9chelicon-wave dry etchingxe2x80x9d) may be used. The helicon wave, which is one type of electromagnetic waves that propagate in plasma, is called a whistler wave and is capable of generating high-density plasma. The use of such a high-density plasma can allow multiple orifices to be simultaneously and accurately form fast and in a predetermined direction.
With the use of the helicon-wave dry etching system, however, the temperature of a target work piece becomes high by the high-density plasma and the orifice plate having thermoplastic adhesive layers adhered to both sides should be used, both of which would raise various problems.
FIG. 3A is a partially enlarged cross-sectional view of a print head before orifices are formed, FIG. 3B is a diagram showing the state where formation of a mask pattern on a metal film is completed, and FIG. 3C is a diagram illustrating a shortcoming which arises at the initial stage of processing orifices by helicon-wave dry etching. As shown in FIG. 3A, the orifice plate 3 has thermoplastic adhesive layers 8a and 8c adhered to both sides of a polyimide film 8b. 
In order to form an ink groove 9 and unillustrated ink flow passages and the like, this orifice plate 3 is placed on a partition 11 with that side of the adhesive layer 8c facing the substrate 1 and is pressed while being heated to 200 to 300xc2x0 C. so as to be fixed onto the silicon substrate 1 as shown in FIG. 3A. Thereafter, the orifice plate 3 is placed in the helicon-wave dry etching system and orifices are formed according to a pattern 15.
The orifice plate 3 with the thermoplastic adhesive layers adhered to both sides thereof is an effectively formed member until it is laminated on the substrate 1. When the pattern 15 is formed with a metal mask film 14 formed on the orifice plate 3 and then helicon-wave dry etching is initiated to apply heat, however, corrugation or rising of a thermoplastic adhesive 8axe2x80x2 at the center portion as shown in FIG. 3C due to a difference between the coefficient of thermal expansion of the thermoplastic adhesive layer 8a at the exposed pattern portion where the metal mask film 14 has been removed prior to the formation (boring) of the orifices and those of the metal mask film 14, the polyimide film 8b and the like. In this case, the greater the exposed area of the pattern portion is, the higher the thermoplastic adhesive layer 8axe2x80x2 rises at the center portion.
If etching progresses in such a situation, the residual of the thermoplastic adhesive layer 8a flows into the ink ejection ports (orifices) so that the ink ejection ports will not be completely round but deformed by the end of the formation of the orifices. At the time of printing, therefore, ink may be ejected in a direction different from the direction it should be ejected, i.e., the direction perpendicular to the surface of the print medium.
Because the opening portions of the holes for connection of bonding wires which correspond to the electrode leads of a drive circuit have relatively large exposed areas, the above phenomenon becomes more noticeable, causing the residual of the thermoplastic adhesive layer 8a to remain a lot. This residual of the thermoplastic adhesive layer 8a causes bonding defects at the time the ink-jet printer head is wire-bonded to the mount substrate.
In any of the cases discussed above, defects reduce the yield, which leads to a cost increase as well as lower working efficiency.
Accordingly, it is an object of the present invention to provide a method of manufacturing an ink-jet printer head, which has a high yield and excellent workability and can efficiently and form multiple ejection nozzles of a good quality in a short period of time without having bonding defects or defective ejection nozzles originated from the residual of a thermoplastic adhesive layer even if a thin film sheet which has an excellent workability and has a thermoplastic adhesive layer adhered to either side thereof is used as the base material for an orifice plate.
To achieve the above object, according to one aspect of this invention, a method of manufacturing an ink-jet printer head having a substrate provided with a plurality of energy generating elements for generating pressure energy for ejecting inks and an orifice plate located on the substrate and having a plurality of ejection nozzles formed therein for ejecting inks in a predetermined direction by pressure generated by the energy generating elements comprises the steps of preparing a thin film sheet material having adhesive layers respectively formed on top and bottom sides, as a material of the orifice plate; removing that one of the adhesive layers which is on an ink-ejecting-side surface of the thin film sheet material; forming an etching mask film on the ink-ejecting-side surface of the thin film sheet material from which the one of the adhesive layers has been removed; forming a pattern corresponding to the plurality of ejection nozzles on the mask film; and forming the plurality of ejection nozzles by dry etching in accordance with the pattern.
According to the above manufacturing method for an ink-jet printer head, the adhesive layers are not thermally expanded at the time of etching and does not adversely affect the etching process. Nor do the adhesive layers remain as a residual after etching. This can prevent bonding defects or defective orifices from being made by such a residual. Further, this method can permit the use of a helicon-wave dry etching system which can implement fast etching with the high-energy ion current, thus making it possible to form a plurality of uniform orifices quickly.
In this manufacturing method, removing of the one of the adhesive layers may be carried out after the thin film sheet material is placed on the substrate or before the thin film sheet material is placed on the substrate. In the latter case, it is preferable that the mask film is formed on the thin film sheet material while the thin film sheet material is being fed between a pair of take-up rolls. This further improves the working efficiency.
In this manufacturing method, the adhesive layers are preferably of a thermoplastic type and more preferably are thermoplastic adhesive layers which have a glass transition point of 150xc2x0 C. or higher.
Further, in the manufacturing method, it is preferable that the mask film is a multilayer mask film having a water repellent composite film, comprised of a water repellent material and metal, and a metal film and that orifices are formed after this mask film is formed on the orifice plate. This modification prevents a plating deposit, which is produced when the composite film is electroplated after forming the orifices, from being adhered to the interior of the head, and improves the yield more. As the water-repellent film can be formed together with the mask film, the working efficiency is increased significantly.
Furthermore, in the manufacturing method, it is preferable that the dry etching is helicon-wave dry etching in view of simultaneous and efficient forming of multiple orifices of the desired shape as mentioned above, or that removing of one of the adhesive layers is carried out by dry etching such as a resist asher.
In addition, the above manufacturing method can effectively be adapted, particularly, to a thermal ink-jet printer in which the energy generating elements are heat generating elements for heating inks to generate bubbles, thereby causing the inks to be ejected.
To achieve the aforementioned object, according to another aspect of this invention, a method of manufacturing an ink-jet printer head having a substrate provided with a plurality of energy generating elements for generating pressure energy for ejecting inks and an orifice plate located on the substrate and having a plurality of ejection nozzles formed therein for ejecting inks in a predetermined direction by pressure generated by the energy generating elements comprises the steps of preparing a thin film sheet material having adhesive layers respectively formed on top and bottom sides, as a material of the orifice plate; placing the thin film sheet material on the substrate; removing that one of the adhesive layers which is on an ink-ejecting-side surface of the thin film sheet material placed on the substrate; and forming the plurality of ejection nozzles by etching on the ink-ejecting-side surface of the thin film sheet material from which the one of the adhesive layers has been removed.
In this manufacturing method, it is likewise preferable that the adhesive layers are of a thermoplastic type. This manufacturing method is particularly effective when it is adapted to a case of forming a plurality of ejection nozzles by helicon-wave dry etching.
Moreover, to achieve the aforementioned object, according to a further aspect of this invention, a method of manufacturing an ink-jet printer head having a substrate provided with a plurality of energy generating elements for generating pressure energy for ejecting inks and an orifice plate located on the substrate and having a plurality of ejection nozzles formed therein for ejecting inks in a predetermined direction by pressure generated by the energy generating elements comprises the steps of preparing a thin film sheet material having adhesive layers respectively formed on top and bottom sides, as a material of the orifice plate; removing that one of the adhesive layers which is on an ink-ejecting-side surface of the thin film sheet material; and forming the plurality of ejection nozzles on the ink-ejecting-side surface of the thin film sheet material from which the one of the adhesive layers has been removed.